1. Field of the Invention
This invention relates to mould sets for use in plastics moulding machines including blow moulding machines and moulding machines which are intended for prototype or other short run purposes. Mould sets are also known as mould bases.
2. Summary of the Prior Art
Plastics injection moulding machines have been known for many years and designs of such machines are available some of which are particularly suited to short run (i.e. less than of the order of 100,000 articles) or prototype manufacture. Hitherto, the mould sets for all types of injection moulding machines have been made mainly of high quality tool steel which is not only a costly material but requires expensive machining operations in order to achieve the required longevity in use. Such mould sets are acceptable from a cost standpoint for long production runs of plastics articles which may reach very large figures. However, when the mould set is only required for comparatively short runs, sometimes very short indeed where prototypes are involved, the cost of the mould sets becomes an unacceptably high proportion of the cost of production of the prototype articles. Such steel mould sets are often built up from individual parts of high quality steel requiring the use of securing means and an assembly operation which may take an appreciable length of time. A typical mould set may incorporate as much as twelve or more main parts, that is excluding guide pins, securing means and so on.
Aluminum tools have been used for short-runs and prototypes at lower cost than steel, but as the design of the tool set is the same as traditional tool sets, such aluminum tools give rise to the following disadvantages:
1. Because the individual plates have to be cut out from large plates and machined to size there is a high wastage of material.
2. The overall design of such aluminum mould sets incorporates more plates to achieve the required standard tool shape, thus again consuming more aluminum.
3. Every mould set needs many similar operations in order to incorporate features of the basic tool, for example, clamping arrangements, cooling channels, raising blocks and so on. This is time-consuming and has to be repeated for every tool.
It is therefore an object of the present invention substantially to reduce the overall cost of tools sets, more especially those intended for prototype and other short duration production runs.